Different between "-DCMAKE_CXX_COMPILER=clang++" and "-DCMAKE_CXX_COMPILER=clang-12"

Code
1

In my environmental, clang and clang++ are all symbolic links to clang-12. And if I use -DCMAKE_CXX_COMPILER=clang++, my C++ codes will linked to stdc++ without problem, but if I use -DCMAKE_CXX_COMPILER=clang-12, it will report errors like this:

Undefined symbols for architecture x86_64:
...
"std::__1::basic_ostream<char, std::__1::char_traits<char> >::sentry::~sentry()", referenced from:
      std::__1::basic_ostream<char, std::__1::char_traits<char> >& std::__1::__put_character_sequence<char, std::__1::char_traits<char> >(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, char const*, unsigned long) in main.cpp.o
...

According to my experience, the compiler (and linker) seems treat my project as a C project, not a C++ one.

So I’m curious what’s the different between -DCMAKE_CXX_COMPILER=clang++and -DCMAKE_CXX_COMPILER=clang-12? Why the former works well but the latter doesn’t, since they are the same (which is clang-12)?

What’s more, I’m using an IDE, which will “cleverly” change -DCMAKE_CXX_COMPILER=clang++ to -DCMAKE_CXX_COMPILER=clang-12. So in this case, what can I do in writing CMake code to make CMake treat my project as a C++? (I tried project(untitled2 CXX) but it doesn’t work).

P.S. I’m using macOs, not sure if this happens on linux.

2

The IDE is wrong. Clang (and GCC) change behavior based on the name by which it is executed. So clang-12 will act as a C compiler and link the C runtime by default. clang++-12 will act as a C++ compiler and link the C++ runtime by default. When compiling C++ with a C compiler (which generally works because $reasons), the C++ standard library must be linked manually.

3

Thanks for helping.

Do you mean that compiler will check the first argument passed in (which is the bin name), to decide to use C or C++ logic?

By the way, I tried to link C++ standard library manually by using set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -stdlib=libc++") but still not working, do you happen to know how to manually set the C++ standard library?

4

Yes, compilers will generally do this.

It depends on the compiler and stdlib in question. You probably need to explicitly say -lc++ or something.